1. Field of the Invention
The field of art to which this invention relates is bipolar surgical instruments, in particular, an improved pivot screw design for bipolar surgical instruments.
2. Description of the Related Art
A technique used extensively in both open and endoscopic surgery is the controlling of bleeding using bipolar electrosurgical instrumentation. The control of bleeding during surgery accounts for a major portion of the time involved in surgery. In particular, bleeding that occurs when tissue is incised or severed can obscure the surgeon's vision, prolong the operation, and adversely effect the precision of cutting. Blood loss from surgical cutting may require blood infusion, thereby increasing the risk of harm to the patient.
Hemostatic electrosurgical techniques are known in the art for reducing bleeding from incised tissue prior to, during, and subsequent to incision. Electrosurgical cutting and coagulating instruments are used to perform such techniques. These instruments can be of a reusable type (which require cleaning and disinfecting or sterilizing before each use) or disposable (which are disposed of after a single use). Each type includes both monopolar and bipolar variations having at least one electrode. Radio frequency (RF) energy is conducted through this electrode to either a remote conductive body-plate (known as a grounding pad) in the case of monopolar instruments, or to a second, closely spaced conductive electrode in the case of bipolar instruments. In monopolar instruments electrical current travels from the electrode through the patient's body to the grounding pad. Bipolar instruments are typically connected to both poles of an electrosurgical generator, therefore current flow is typically limited to tissue adjacent to the working end of the bipolar instrument (where the two electrodes are located).
Bipolar electrosurgical instruments typically comprise two halves which pivot about a pivot means such as a pivot screw. However, pins and rivets are also utilized as the pivot means. Each halve comprises an electrode which needs to be electrically isolated from the other half. Isolation of the instrument halves is typically achieved by either coating a metallic pivot screw with an insulating material or fabricating the pivot screw entirely from an insulating material. In addition, surfaces of the two halves which are in sliding contact with each other are insulated, typically by coating the common surfaces with an insulating material, such as alumina oxide.
FIGS. 1 and 2 illustrate a bipolar surgical instrument of the prior art, and generally referred to as reference numeral 100. The bipolar surgical instrument 100 typically comprises a first and a second half 102, 104. Each half has a distal end 102a, 104a at which an end effector, such as scissor blades, are disposed. Each half also has a proximal end 102b, 104b at which an actuating means is disposed, such as finger loops 106, 108. Each instrument half comprises an electrode, whereby RF energy of differing polarity is supplied to each half through connector posts 110, 112 disposed at the proximal end 102b, 104b of the instrument halves 102, 104. The two halves 102, 104 engage in sliding contact at first and second pivot surfaces 114, 116 and are fastened together at the pivot surfaces 114, 116 by a fastening means, typically a pivot screw 118 disposed in a first and second bore 120, 122. The pivot screw has a head 118a and a first threaded portion 118b. The first bore 120 being in the first half 102, the second bore 122 being in the second half 104 and opposing the first bore 120.
To electrically isolate the two halves from each other, a layer of insulating material 124 is disposed between the first and second halves at their sliding surfaces. If the screw 118 is a conductive material, such as aluminum, it is further coated with an insulating material to electrically isolate the two instrument halves from each other. Additionally, the instrument is typically coated with an insulating material 126 in all portions other than the end effectors so as to insulate a user from electrical shock.
As can be seen in FIG. 2, the second bore 122 typically has a second threaded portion 128, whereby the first bore 120 is typically sized as a through hole to accommodate easy passage of the first threaded portion 118b of the pivot screw 118 but which captures the head 118a of the pivot screw 118. The screw 118 is disposed through the first bore 120 where the first threaded portion 118b engages with the second threaded portion 130 of the second bore 122 to provide a positive locking of the two halves.
Coated aluminum screws with an anodized coating are typically used in the art. While they have the advantage of being able to withstand the physical abuse typically encountered during surgery and processing (cleaning, disinfecting, and sterilizing), they suffer from a number of disadvantages. The most serious of which is the loss of portions of the coating due to rubbing contact between mating surfaces. Because the screw head 118a moves relative to the instrument half 102, the screw coating is subject to wear. An uncoated portion of the screw or a chipped portion of the screw's insulating coating can lead to an eventual shorting across the screw and between the instrument halves. This will result in a very low resistance between instrument halves. Consequently, the voltage maintained between the instrument halves will not be sufficient to effect adequate hemostasis. The greater the worn portion is in size, the more significant the degradation of the hemostasis performance.
Ceramic coated screws, such as alumina oxide coated on aluminum, are also used as the pivot screw in a bipolar surgical instrument. However, ceramics are brittle and prone to chipping. As discussed, chipping of the insulating coating can lead to poor or inadequate hemostasis. Furthermore, ceramic coated screws do not easily thread into a mating female thread because of its high coefficient of friction. Impregnating, the screw with a material having a lower coefficient of friction, typically a polymer, helps with the latter problem. However, the impregnation does little to solve the former problem and adds significant costs to the fabrication of the screws.
Pivot screws fabricated entirely from ceramic or an impregnated ceramic also have their drawbacks. Ceramic screws are brittle and susceptible to failure when subjected to external forces caused by mishandling of the instrument. For instance, dropping the instrument from an instrument table to a hard operating room floor can result in the fracturing of the ceramic pivot screw, resulting in instrument failure.
Plastic screws have also been contemplated as pivot screws in bipolar surgical instruments. Like ceramic screws, plastic screws cannot withstand the impact stresses associated with mishandling the instrument, such as when the instrument is dropped onto a hard surface. Additionally, plastic screws cannot withstand expected torque levels experienced during normal use which is needed to adequately hold the two instrument halves together. Not only do plastic pivot screws suffer from being susceptible to failure from impact and torsional stresses, they can also fail electrically. Plastic screws have been found to fail from carbon tracking due to the high voltages used in bipolar electrosurgical instruments. Typically, the voltages run as high as 1,500 volts (peak to peak). At such elevated voltages, plastic screws can burn and/or melt causing catastrophic failure of the bipolar instrument.
Besides electrical conduction between instrument halves due to worn or chipped insulation on the screw 118, electrical conduction can occur directly between instrument halves 102,104 as a result of exposed portions of the pivot surfaces 114,116. If the insulating material 124 disposed on one or both of the pivot surfaces 114, 116 is chipped around or near the pivot screw 118, poor hemostasis will result. Such a chipped area, leaves portions of the pivot surfaces 114,116 exposed. An insulating material 124 having a chipped area 132 is shown in FIG. 2. When the gap associated with the chipped area 132 is filled with an electrically conductive liquid (e.g., isotonic saline or blood) and the resulting exposed pivot surface areas are sufficiently large while the gap spacing is small, the resistance between the instrument halves 102, 104 can become small. As a consequence, there is low voltage between the instrument halves resulting in poor hemostasis until the conductive liquid boils away. If the chipped portion 132 is around the first and/or second bores then the exposed area can be come much larger and the associated resistance much lower.
Accordingly, there is a need in the art for electrosurgical instruments having an improved pivot screw design which can withstand the physical and electrical rigors associated with bipolar instrumentation, and which also provide an effective isolation between electrodes.
Furthermore, there is also a need in the art for electrosurgical instruments having an improved pivot screw design in which the likelihood of electrical conduction between instrument halves great enough to influence effective hemostasis is decreased.